Molecular biology of positive strand RNA viruses

Category Archives: DWV

We are conducting a trial of coordinated Varroa treatment in conjunction with the beekeepers on the Isle of Arran. In late September DJE and Luke Woodford – the EastBIO-funded student leading the project – visited Arran to present an evening lecture on Varroa and DWV: Science and Practical Beekeeping.

Our studies exploit our understanding of changes in the virus population associated with Varroa transmission (rather than transmission from bee to bee during feeding) to monitor the ‘health’ of the colony.

The talk was followed by an extended question and answer session covering the project and more general aspects of beekeeping and Varroa control.

The Isle of Arran was looking fantastic as we crossed from Ardrossan on the CalMac ferry. Goatfell, the highest point on the Arran horseshoe ridge (see image above) is a great walk and thoroughly recommended.

Our snappily-titled manuscript “The Iflaviruses Sacbrood virus and Deformed wing virus evoke different transcriptional responses in the honeybee which may facilitate their horizontal or vertical transmission” has just been published in PeerJ. We analysed changes in the transcriptome following infection with deformed wing virus (DWV) and sacbrood virus, or DWV alone. We propose that the difference in expression we observed of the honeybee immune genes induced by SBV and DWV may be an evolutionary adaptation to the different predominant transmission routes used by these viruses .

On Thursday 14th January I’m talking at an evening meeting of Fife Beekeepers Association about the biology of Deformed Wing Virus and how our understanding of the virus should help devise more rational integrated pest management strategies. This is the first of several outreach events planned for 2016 in which our BBSRC-funded research on honeybee viruses will be discussed.

Not long now until the beekeeping season starts and we can get on with our planned field studies 🙂

During previous research on deformed wing virus (DWV) biology and its transmission by Varroa I’ve moved known Varroa-free colonies (sourced from a region of the UK which the mite has yet to reach and maintained totally mite-free) into apiaries in the countryside. Within 2-3 weeks Varroa was detectable in sealed brood, showing that mite infestation occurs very readily. I know other researchers who have made very similar observations. Where do these mites come from?

They’re not all ‘your’ bees

The obvious source would be the phoretic mites transported on workers ‘drifting’ from nearby infested colonies, or on drones which are known to travel quite long distances and may be accepted by almost any colony. If you want to see how frequent this is try marking a few dozen drones with a dab of paint. To avoid confusion use the colour used to mark queens next year. There are unlikely to be 4+ year old queens in the apiary and the drones will all perish before the end of the current season. Over the next few days and weeks the drones will appear in adjacent colonies, and some will likely leave the apiary and be accepted in your neighbours colonies.

Hives in rows …

Beekeepers are usually aware that colonies at the ends of rows often ‘accumulate’ bees that have drifted when returning to the hive. In shared association apiaries some crafty beekeepers will site their colonies at the ends of rows to take advantage of the ‘generosity’ of other colonies. However, many beekeepers probably do not appreciate the extent to which drifting occurs. Pfeiffer and Crailsheim report (1998) that 13-42% of the population of a colony are ‘alien’ i.e. have drifted from adjacent hives, depending upon the time of season. Remember that drifting occurs in both directions simultaneously, so the overall numbers of bees in a colony may not be adversely affected (or boosted). In other studies Sekulja and colleagues report (2014) that ~1% of marked bees drifted between colonies over a three day observation window. Interestingly, American foulbrood (AFB) infected bees drifted slightly more than uninfected bees. Spread of foulbroods during drifting is one reason the bee inspectors check nearby apiaries when there is an outbreak. These studies were all on workers where drifting primarily occurs during orientation flights before the bees become foragers. Drones drift two to three times more than workers (Free, 1958).

The likelihood of drifting must be closely related to the separation of hives and apiaries. Although workers will forage up to 2-3 miles from the hive I suspect the proportion of bees that drift this distance is small to undetectable. Drones are known to fly up to about five miles to reach drone congregation areas for queen mating and are accepted by all colonies. I’ve regularly found drones appearing in (relatively) isolated mini-nucs. I’m not aware of studies that have formally tested drifting between apiaries (though it is reported in passing in the Sekulja et al., 2014 paper referenced above).

Consequences of drifting

So, your hives contain workers and drones from many nearby colonies, and you can only really be sure that they’re all “your” bees if you live – as the sole beekeeper – on an isolated island. Not only does your neighbour generously exchange bees with you, he or she also kindly shares the phoretic mites those bees are carrying, the viral payload the bees and mites are infected with and – if you’re really unlucky – the Paenibacillus larvae spores responsible for causing AFB infection (and vice versa of course).

There are lessons here that should inform the way we conduct our integrated pest management to maintain healthy colonies.

This post provides background information for an article (“Viruses and Varroa: Using our current controls more effectively” by David Evans, Fiona Highet and Alan Bowman) in the December 2015 issue of Scottish Beekeeper, the monthly magazine for members of the Scottish Beekeepers Association.

I’m delighted to be talking at the Hampshire Beekeepers Association autumn convention at Sparsholt College this weekend. This is the first of several ‘winter talks’ to BKAs about our research on deformed wing virus and Varroa. Time permitting I hope to discuss some forthcoming studies on coordinated Varroa control that we’re doing with Alan Bowman (Aberdeen) and Fiona Highet (SASA) and that will shortly be featured in the Scottish Beekeeper. I was invited to talk at this event before accepting a post in St. Andrews … it’s a long way to travel. However, one of the advantages of flying to these events is I can’t be tempted by too many goodies from the trade stands 😉

Late last week, in the dark and rain, the first two honeybee colonies were installed in the bee house on our research apiary. The warm(ish) and dry environment will greatly benefit our research by helping us harvest larvae and pupae whatever the weather conditions are outside. In addition, we expect brood rearing by the colony to be extended earlier and later in the season, so enabling us to undertake more extensive studies of the biology of deformed wing virus.

The bee shed has special windows – just about visible in the poor quality cellphone picture – that allows the bees that leave the hive when the roof is removed to ‘escape’ from the shed … they can then re-enter the hive via a tunnel entrance through the shed wall.

We have recently submitted a paper to PeerJ on gene expression changes resulting from deformed wing virus and sacbrood virus infection. A pre-print of this manuscript can be viewed on the PeerJ website.

Abstract

Sacbrood virus (SBV) and deformed wing virus (DWV) are evolutionarily related positive-strand RNA viruses, members of the Iflavirus group, which infect the honeybee Apis mellifera, but have strikingly different levels of virulence when transmitted orally. Honeybee larvae orally infected with SBV usually accumulate high levels of the virus, which halts larval development and causes insect death. In contrast, oral DWV infection at the larval stage usually causes asymptomatic infection with low levels of the virus, although high doses of ingested DWV could lead to DWV replicating to high levels. We investigated effects of DWV and SBV infection on the transcriptome of honeybee larvae and pupae using global RNA-Seq and real-time PCR analysis. This showed that high levels of SBV replication resulted in down-regulation of the genes involved in cuticle and muscle development, together with changes in expression of putative immune-related genes. In particular, honeybee larvae with high levels of SBV replication, with and without high levels of DWV replication, showed concerted up-regulated expression of antimicrobial peptides (AMPs), and down-regulated expression of the prophenoloxidase activating enzyme (PPAE) together with up-regulation of the expression of a putative serpin, which could lead to the suppression of the melanisation pathway. The effects of high SBV levels on expression of these immune genes were unlikely to be a consequence of SBV-induced developmental changes, because similar effects were observed in the honeybee pupae infected by injection. We suggest that the effects of SBV infection on the honeybee immunity could be an adaptation to horizontal transmission of the virus. Up-regulation of the expression of AMP genes in the SBV-infected brood may contribute to protection of the SBV virus particles in dead larvae from bacterial degradation. Suppression of the melanisation may also reduce the loss of infectivity of SBV in the larvae. Therefore it is possible that activation of AMP expression and suppression of melanisation could increase ability of SBV to be transmitted horizontally via cannibalization route. We observed no changes of AMPs and the melanisation pathway genes expression in the orally infected larvae with high levels of DWV replication alone. In the injected pupae, high levels of DWV alone did not alter expression of the tested melanisation pathway genes, but resulted in up-regulation of the AMPs, which could be contributed to the effect of DWV on the regulation of AMP expression in response to wounding. We suggest that the effects of single DWV infection on the expression of these immune-related genes could reflect evolutionary adaptations of DWV to vertical transmission. Up-regulation of AMPs is costly and suppression of melanisation may increase susceptibility to infections, therefore these changes may have negative impact on honeybee survival and, consequently, of the survival of DWV.

I’m delighted to be sharing the programme with Michael Palmer and Celia Davies at the Somerset BKA lecture day this Saturday (21st February ’15). I’ll be adding a small bit of science to the day and no doubt benefiting significantly from their wealth of beekeeping expertise. It should be a very enjoyable event.

Update – it was a very enjoyable event. Aside from a few audio problems with a misbehaving microphone a packed hall enjoyed two talks by Celia Davies on Summer and Winter Bees and A World of Scents and a further two from Michael Palmer on the Sustainable Apiary and Queen rearing. If you’ve not heard Michael talk about the importance of overwintering nucs for sustainable beekeeping then you should either try and catch him on his current UK tour or watch him deliver the talk at the National Honey Show on YouTube. I think I’ve heard the talk three times now and have learnt something new every time. All the talks – including our contribution on the science of Varroa and deformed wing virus – generated lots of questions and discussions. With thanks to Sharon Blake for the invitation and organisation of the day.

I’m delighted to be speaking at the CABK Stratford Conference (the Central Association of Beekeepers; Bringing Science to the Beekeeper) on Saturday and Sunday 22/23 November 2014. I’ll be discussing the identification of a virulent strain of deformed wing virus, characteristics of its transmission and potential ways it might be controlled in the future. The CABK website doesn’t yet appear to list other speakers, but the provisional programme I’ve seen lists Alison Haughton from Rothamsted, Ben Jones from FERA, Jochen Plugfelder from Bern and Bob Smith from Kent.

There should be ample time for discussions so please introduce yourself if you want to chat.